Influenza virus causes worldwide seasonal infections and occasional pandemics with high mortality rate. Human viruses are known to have a preference for ?2-6 linked sialic acids (NeuAc?2-6Gal), while avian viruses exhibit a preferenc for ?2-3 linked sialic acids (NeuAc?2-3Gal). This difference in receptor specificity is widely considered a major species barrier for transmission of avian viruses in the human population. Although this binary model of receptor specificity has been useful, it belies the true complexity o sialic acid containing glycans on host cells, it has becoming increasingly limiting since recent influenza viruses exhibit mixed specificities that are not distinct from avian viruses using standard assays of assessing receptor specificity. The use of glycan microarrays with dozens of ?2-3 and ?2-6 linked glycans has revealed that influenza viruses exhibit dramatic differences i their ability to recognize individual glycans within those broad groups. However, interpretation of these findings is confounded by the fact that there is little information on the types of glycans that are actually present on human airway epithelium, and whether the relevant glycans are represented on glycan microarrays. To address this gap in knowledge, we intend to 1) analyze the glycan structures on human airway epithelial cells, 2) to build a synthetic library of these glycans for constructing a custom glycan microarray, and 3) to evaluate the specificity of human influenza virus hemagglutinins (HAs) and neuraminidases (NAs) to identify receptor-binding properties that support their ability to transmit in humans. This information will identify recepto determinants on the human airway that are shared by human influenza viruses that transmit in the human population, and shed light on properties of the HA and NA that contribute to pandemic risk of influenza viruses from avian viruses that occasionally infect humans.